Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$134.63	11.546%	$150.1744	$150.17	$150.15	$150.20
Purchase #2	$211.38	5.655%	$223.3335	$223.33	$223.35	$223.30
Purchase #3	$131.32	6.872%	$140.3443	$140.34	$140.35	$140.30
Purchase #4	$223.66	11.860%	$250.1861	$250.19	$250.20	$250.20
Purchase #5	$35.50	11.759%	$39.6744	$39.67	$39.65	$39.70
Purchase #6	$40.62	4.203%	$42.3273	$42.33	$42.35	$42.30
Purchase #7	$153.99	12.765%	$173.6468	$173.65	$173.65	$173.60
7 purchase totals =	$931.10		$1,019.6868	$1,019.68	$1,019.70	$1,019.60